1. Field of the Invention
The present invention is related to an image processing apparatus capable of preventing unauthorized disabling of the copy protect function of video and other contents signals and a system and a method of the same.
2. Description of the Related Art
Players for video contents signals of video home system (VHS) tapes, digital versatile disks (DVD), etc. are equipped with a copy protect function preventing the output contents signals from being normally recorded by interfering with the operation of automatic gain control (AGC) circuits.
FIG. 5 is a view for explaining a DVD system 1 of a related art of the present invention.
As shown in FIG. 5, the DVD system 1 comprises a DVD reproduction unit 2, a central processing unit (CPU) 3, and an image processing unit 4.
The DVD reproduction unit 2 outputs a contents signal S2a obtained by playing a DVD to the image processing unit 4.
The CPU 3, for example, is connected to the image processing unit 4 via an I2C (Inter Integrated Circuit) bus 8, outputs a clock signal CLK as critical data S3a to the image processing unit 4, and transfers data with the image processing unit 4.
The image processing unit 4, as shown in FIG. 5, comprises an I2C_IF circuit 10, an encoder 11, and a copy protect circuit 12.
The I2C_IF circuit 10 outputs control data S10b obtained based on control data S3a input from the CPU 3 to the encoder 11 at a timing based on the clock signal CLK input from the CPU 3 via the I2C bus 8 and also outputs control data 10c to the copy protect circuit 12.
The encoder 11 encodes the contents signal S2a input from the DVD reproduction unit 2 based on the control data S10b input from the I2C_IF circuit 10 and outputs a contents signal S11 obtained by the encoding to the copy protect circuit 12.
The copy protect circuit 12 performs copy protect processing on the contents signal S11 based on the control signal S10c from the I2C_IF circuit 10 and outputs a contents signal S4 obtained by the copy protect processing to a display 5.
At this time, in the copy protection processing, the copy protect circuit 12, for example, inserts a pulse signal randomly changing in amplitude in a vertical blanking period of the contents signal S11 to produce the contents signal S4.
Due to this, when attempting to input the contents signal S4 to a video recorder to make an unauthorized copy, the pulse signal inserted in the contents signal S11 will cause the AGC circuit in the video recorder to malfunction and cause flickering of the reproduced screen, horizontal distortion, and other pronounced degradation of an image when playing back the copied contents signal.
Further, as shown in FIG. 6, in order to prevent a dummy circuit 15 from being illicitly inserted between the CPU 3 and the image processing unit 4, the control data S3a output from the CPU 3 to the I2C bus 8 from being intercepted, and the I2C_IF circuit 10 from being illicitly modified for the purpose of invalidating the copy protect function of the copy protect circuit 12, the DVD system 1 is equipped with a function verifying a destination of an output of the control data S2a by the CPU 3.
Specifically, the CPU 3 reads identification data ID of the I2C_IF circuit 10 stored in a predetermined read register RR[n] in the I2C_IF circuit 10 via the I2C bus 8 at a predetermined timing and verifies this to confirm that the destination of output of the control signal S2a is the legitimate I2C_IF circuit 10, that is, that a dummy circuit 15 is not inserted.
In the conventional DVD system 1 described above, however, the identification data ID transmitted from the I2C_IF circuit 10 to the CPU 3 is the same every time; therefore, it is easy to intercept the identification data ID by the dummy circuit 15 shown in FIG. 6 and thereby fabricate a dummy circuit 15 having the function of transmitting the predetermined identification data ID in response to an inquiry from the CPU 3.
Due to this, there is the disadvantage that the control data S2a is liable to be illicitly analyzed by using such a fabricated dummy circuit 15.